If TOR had the ability to make a custom companion that would be one of your alts, I know I'd have on the republic side my sage and my imperial side would be my sorc. Mainly so I could have a force using healer.
What would you pick and why?
Let me first say that would be an AWESOME feature to the game!
I'd probably have my Merc as my main and my Sniper as a companion. I love having HK for a companion but my sniper would be a nice substitute.